Arsenic-antimony-bismuth hollow cathode lamp

ABSTRACT

A radiation source of the hollow cathode variety capable of emission of spectral radiation characteristic of the elements arsenic, antimony and bismuth.

0 United States Patent [151 3,648,092 Wooldridge et al. 51 Mar. 7, 1972[54] ARSENIC-ANTIMONY-BISMUTH HOLLOW CATHODE LAMP [56] f r n Ci [72]Inventors: James E. Wooldridge, Elmira Heights; UNITED STATES PATENTSGems Yammki, Hmeheads, 3,361.925 1/1968 Vollmer ..313/209 x 3,412,27811/1968 Sebensetal. ..3l3/346 [73] Assignee: Westinghouse ElectricCorporation, Pitt- Sburgh, Primary ExaminerRaymond F. l-lossfeldAttorney-F. H. Henson and C. F. Renz 1221 Filed: Apr. 13, 1970 1211Appl. No.2 27,697 [57] ABSTRACT A radiation source of the hollow cathodevariety capable of 521 u.s.c1. ..3l3/209,3l3/2l8,3l3/346R jgfijgg" gfjff f figfigfggig' elements 511 1111.01 ..l-l01j6l/04 [58] Field ofSearch ..3l3/209, 218, 346 4 Claims, 1 Drawing Figure JLQ I l 2s 22Patented March 7,1972 3,648,092

WITNESSES INVENTORS James E. wooldridge and George K. Yum oki BY// V fiATTORNEY ARSENIC-ANTIMONY-BISMUTII HOLLOW CATI-IODE LAMP BACKGROUND OFTHE INVENTION This invention relates to electron discharge devices ofthe hollow cathode type which are adapted for emitting radiation havingdefined spectral lines dependent upon the material within the cathode.One particular application of these light sources is in spectroscopicinvestigations. There have been considerable numbers of hollow cathodedevices provided which both emit radiation of a single element or emitradiation of several elements from a common cathode. In the case of theelement arsenic, the prior art practice was to place a lump of thiselement inside a cup-shaped cathode. The cup-shaped cathode was of ahigh-melting point material such as iron. It was also possible tomachine a cathode from a pure slug of arsenic. While these cathodes didproduce the spectral lines of the arsenic, they did exhibit severalproblems. The vapor pressure of arsenic is high and therefore theoperating current of the device has to be kept at a low value. If thisis not done, rapid destruction of the cathode could occur..It is alsofound that the spectral output, which is related to operational current,suffers because of the current limitation. The high-vapor pressure ofarsenic at the operating temperature also causes excessive evaporationof the cathode material and its deposition on the internal structure ofthe lamp. This can cause electrical shorts or erratic discharges in thedevice after a few hours of operation. The cathode material also canvaporize and coat the surface of the output window of the lamp andthereby reduce the transmission of light through the window.

It is accordingly a general object of this invention to provide a newand improved hollow cathode for use in the spectral radiation devicecapable of emission of spectral lines of the particular elementsarsenic, antimony and bismuth.

SUMMARY OF THE INVENTION A new and improved hollow cathode devicecomprising a cathode comprised of a metallic substance of arsenic,antimony and bismuth and in which the arsenic consists of about 25 to 75percent by weight, the antimony about to 50 percent by weight and thebismuth less than 30 percent by weight of the metallic substance.

DESCRIPTION OF THE DRAWING For a better understanding of the invention,reference may be had to the preferred embodiment, exemplary of theinvention, shown in the accompanying drawing which is a perspectiveview, partially broken away and partially in section of a dischargedevice embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing,there is shown an electron discharge device 10 in accordance with thepresent invention. The electron discharge device 10 includes an envelope11, made of a suitable insulating material such as glass and having anenlarged tubular portion 12 and a smaller tubular portion 14 which areinterconnected by a transition portion 13. The tubular portion 14 issealed off at one end by a window 16 which is made of a suitablematerial such as U.V. glass, quartz, magnesium fluoride, lithiumfluoride to name a few for efficiently transmitting radiationwavelengths produced by the device. The tubular portion 12 is sealed offby a button stem 18 with a tipped off exhaust tubulation 20 in a mannerwell known in the art. I

A cathode element 22 which is comprised of a metallic substance ofarsenic, antimony and bismuth is provided within the envelope 11. Thecathode element 22 is cup-shaped and may be of cylindrical configurationhaving a centrally extending opening of about one thirty-second to onehalf inch in diameter or hollow portion 24 extending from an edge 23 ofthe cathode element 22 facing the window 16' into the cathode element 22for a length of about A; to 2 inches. The cathode element 22: may besupported by an electrically conductive lead 26 made up of suitablematerial such as nickel. The lead 26 may be affixed to the cathodeelement 22 and extends through the stem header 18 to the exterior of theenvelope 11. The lead 26 provides not only the support for the cathode22 but means of applying a potential to the cathode 22.

An anode element 28, which is illustrated as a ring member is positionedin close proximity to the cathode element 22 at its upper edge '23. Theanode element 28 is made of a suitable electrically conductive materialsuch as tantalum and is supported within the envelope by means of the 2support leads 30. At least one of the support rods 30 is of anelectrical conductive material such as nickel. The rods 30 are securedto the anode 28 and are supported and secured through the button stem18. A' potential may be applied to one of the support rods 30 forapplication of potential to the anode.

In order to limit the path of electrical discharge between the cathodeelement 22 and the anode element 28, shielding means are provided whichinclude two insulating discs 38 and 44 which are disposed in a spacedparallel relationship between the cathode element 22 and the anodeelement 28. More specifically, the insulating disc 38 has an aperture 40therein which is disposed concentrically about the hollow portion 24 ofthe cathode element 22. Further, the insulating disc 38 may be disposedso as to be in close proximity to or abut with the upper edge 23 of acathode element 22 and extend therefrom to the inner surface of theenvelope 1!. The second insulating disc 44 has an aperture 41 into whichthe cathode 22 is positioned and the disc 44 extends from the outersurface of the cathode 22 to the inner surface of the envelope 1]. Inaddition, the shielding means includes a pair of insulating sleeves 48disposed about the support rods 30 and extending between the button stem18 and the insulating disc 44. Insulating rings 47 are disposed aboutthe support rods 30 between the insulating discs 44 and 38 andinsulating rings 46 are disposed about the rods 30 between theinsulating disc 38 and the anode element 28. A more detailed descriptionof the structure may be found in US. Pat. No. 3,264,5ll entitledLow-Discharge Device by G. K. Yamasaki.

The envelope 11 is exhausted and a suitable gas such as argon or neon isprovided therein at a pressure of about 1 mm. of Hg. to 30 mm. of Hg.

In the operation of the device, suitable potentials are applied betweenthe cathode 22 and the anode 28 so that an electrical discharge occursbetween the cathode element 22 and the anode element 28 through thegaseous medium within the envelope 11. This discharge creates positiveions of gas which in turn'bombard the inner surface of their opening 24of the cathode element 22 thereby sputtering excited atoms of the threematerials off of the walls of the opening 24. These excited atoms emitlight of wavelengths characteristic of three materials, namely arsenic,antimony and bismuth. This light is emitted through the window 16.

A method of manufacturing the cathode element 22 may be as followsi Thestarting materials for the constituents may have a purity of about 99.99percent and approximately 4 to +20 mesh size. One specific combinationof materials for the cathode element 22 consists of 40 percent arsenic,40 percent antimony and 20 percent bismuth by weight. The materials areweighed out in the above ratio and intimately mixed together and thenmay be placed in a vycor bulb of approximately eleven thirty-secondinches inside diameter and about 6 inches long. The bulb may then beevacuated to about 10 torr and sealed off. The bulb must be under anegative pressure because of the high-vapor pressure of molten arsenic.This vapor pressure is gradually reduced as the arsenic reacts with theantimony and bismuth. After the bulb has been sealed off, it is placedin a furnace and heated to about 300 C. and held there for 15 minutes.It is then taken to a temperature of about 600 and held for 15 minutesand then to about 800 C. for 30 minutes. The material is completelymolten at about 650 to 700 C. In order to help mix the constituents, thefurnace may be slowly rocked during the 30 minute period at thetemperature of 800 C. The additional heat is to ensure that the mixtureis in a molten state. After completion of the heating cycle the furnaceis cooled down at a rate of about 2 per minute and the resultingmetallic substance is cast into a solid rod when it is cooled. The vycortubing may be broken away and the rod machined into the cathode element22.

[t has been found that for practical reasons the arsenic must be 25 to75 percent by weight, the antimony to 50 percent by weight and thebismuth less than 30 percent by weight of the metallic substance. Theaddition of antimony primarily determines the operational current of thedevice by having the effect of lowering the effective vapor pressure ofthe arsenic in the metallic substance. It also effectively decreases theelectrical resistance of the cathode. One is then able to operate athigher currents without excessive vaporization of the arsenic. Forexample, operational currents of milliamperes have been utilized for aperiod of 900 hours time without destruction of the cathode. Theaddition of bismuth is to primarily improve the machinability of acathode and to reduce the drift in the arsenic spectral output withrespect to operational time of the cathode.

It will therefore, be apparent that there has been disclosed a hollowcathode discharge device comprised of a cathode which will generatespectral emission representative of the three elements arsenic, antimonyand bismuth. The wavelengths of emission of most common interest and useare Asl,937A. and 1,972A., Sb-2,068A., 2,311A. and

Bi2,230A., 3,068A.

We claim as our invention:

1. A radiation source of the hollow cathode type comprising an anode anda cathode positioned within an envelope with a gas filling, said cathodeincluding a metallic substance of arsenic, antimony and bismuth fromwhich spectral emission characteristic of arsenic, antimony and bismuthis desired, said metallic substance comprised of about 40 percent byweight of arsenic, about 40 percent by weight of antimony and about 20percent by weight of bismuth.

2. The radiation source of claim 1 in which said cathode is a cup-shapedmember consisting essentially of said metallic substance.

3. A radiation source of the hollow cathode type comprising an anode anda cathode positioned within an envelope with a gas filling, said cathodeincluding a metallic substance consisting essentially of arsenic,antimony and bismuth from which spectral emission characteristic ofarsenic, antimony and bismuth is desired, said metallic substanceconsisting essentially of about 25 to 75 percent by weight of arsenic,about 15 to 50 percent by weight of antimony, and less than about 30percent by weight of bismuth.

4. The radiation source of claim 3 in which said cathode is a cup-shapedmember consisting essentially of said metallic substance.

2. The radiation source of claim 1 in which said cathode is a cup-shapedmember consisting essentially of said metallic substance.
 3. A radiationsource of the hollow cathode type comprising an anode and a cathodepositioned within an envelope with a gas filling, said cathode includinga metallic substance consisting essentially of arsenic, antimony andbismuth from which spectral emission characteristic of arsenic, antimonyand bismuth is desired, said metallic substance consisting essentiallyof about 25 to 75 percent by weight of arsenic, about 15 to 50 percentby weight of antimony, and less than about 30 percent by weight ofbismuth.
 4. The radiation source of claim 3 in which said cathode is acup-shaped member coNsisting essentially of said metallic substance.